Patent pledge
A public promise by a patent holder not to sue certain users – usually open source projects – for infringement.
IBM kicked things off in 2005 by pledging not to assert 500 patents against open source. Microsoft followed in 2006 with the Open Specification Promise covering its file formats and protocols, Google launched its Open Patent Non-Assertion Pledge in 2013, and Tesla announced in 2014 that it wouldn't sue anyone using its technology "in good faith". These are one-sided: no licence is signed, but a public promise makes it awkward to argue the opposite in court later.
The fine print decides what they're worth. Most pledges carry a defensive clause that falls away if the recipient sues the pledger, and "good faith" is defined by whoever made the promise. A patent pledge is a ceasefire, not disarmament.